Serglycin-dependent mast cell-specific proteases and their potential interactions with Giardia intestinalis

Sammanfattning: Mast cells are located in mucosal and connective tissues throughout the body where they play important roles in immune reactions towards infections. Mast cell deficiency results in failure of clearance of the non-invasive intestinal protozoan parasite Giardia intestinalis in mice, but the mast cell-driven mechanisms remain poorly understood. It is well known that pathogen-activated mast cells can release large number of inflammatory mediators, including the mast cell specific proteases and the serglycin (SG) proteoglycan. In this thesis the functional roles of the SGdependent mast cell proteases tryptase and chymase during G. intestinalis were addressed, both in vitro and in vivo. In vitro, soluble Giardia proteins (sGPs) were demonstrated to stimulate mucosallike mast cells to release IL-6 and tryptase, and both sGPs and excretory-secretory proteins (ESPs) were found to enhance human and mouse tryptase activity, but in contrast sGPs inhibited chymase activity. These finding suggest that proteins secreted by Giardia can modulate the activity of both chymase and tryptase. In vivo, oral gavage with Giardia trophozoites was performed to challenge chymase mMCP-4-deficient as well as SG-deficient mice. Clinical scoring and weight data were recorded in a blinded fashion. Fecal samples collected from individual mice every second day were evaluated with nested PCR to confirm successful Giardia infection. The small intestines, serum and tail tissue were sampled from each mice and evaluated for: cytokine and chemokine expression, morphological changes and genotype. Infection of mature adult mice with G. intestinalis caused a more rapid significant weight loss in the mMCP-4-deficient than in the mMCP-4 +/+ mice. In young SG-deficient female mice the infection with G. intestinalis caused a significantly reduced weight gain, suggesting a sex- and SG-dependent response to the infection. Serum levels of IL-6 matched the weight changes in both the mMCP-4 and the SG mouse strains. A regulatory role of mMCP-4 and SG, respectively on the intestinal inflammatory cytokine responses was indicated by real-time PCR. Furthermore, increased numbers of intestinal goblet cells and granulocytes, unaltered myeloperoxidase activity and a decreased neutrophil elastase activity were found in the G. intestinalis-infected mice, suggesting that secreted Giardia proteins can also modulate neutrophil protease activities.